1. Field of the Invention
The present invention relates to a pipe connecting device which is preferably used in piping for a liquid having high purity or ultrapure water to be handled in a production process of various technical fields such as production of semiconductor devices, production of medical equipment and medicines, food processing, and chemical industry, and which is used as means for connecting a fluid apparatus such as a pump, a valve, or a filter, or a tube that is a fluid transfer path.
2. Explanation of Related Art
As a pipe connecting device (pipe joint) of this kind, for example, a pipe connecting device disclosed in Patent Literature 1 is known. Namely, the disclosed resin pipe joint has a configuration where, by a screw advancement of a union nut (2) caused by screwing an internal thread (8) to an external thread (5) in a state where a tube (3) is externally fitted to a fitting cylinder (4) of a joint body (1) to form a flared portion (3A), a tube pressing portion (seal pressing portion: 10) is caused to press a flaring changing region (9).
In the pipe connecting device disclosed in Patent Literature 2, the worker holds a union nut in the hand and fingers, and then rotates and fastens the union nut, thereby connecting a tube to a joint body in a sealed state. In order to allow the fastening torque to be transmitted as easily as possible, small antislip asperities (knurling) are continuously formed on the outer periphery of the union nut in the circumferential direction.
In the configuration where the means for manually rotating and fastening the union nut is employed, a tool for rotation is not necessary, and there is no inconvenience that, when the worker forgets to bring the tool, the operation is disabled. The pipe connecting device has an advantage that the pipe connecting device can be assembled easily and conveniently. In order that a nut for the pipe joint is sufficiently fastened by an operation force manually applied by the worker so as to attain a satisfactory seal, however, an accordingly large force is required, and there are disadvantages such as that the nut is not suitable for connecting large pipes, and that workers are often limited.
As disclosed in Patent Literature 3, on the other hand, a tool by which a union nut can fastened satisfactorily and firmly in simple operation is provided. When a hook wrench which is a rotary tool is used, a union nut can be firmly fastened although the tool operation is performed in a relatively simple manner. Therefore, the tool has an advantage that a pipe connecting device can be assembled irrespective of whether the worker has a sufficient physical strength or not, or whether the worker is skillful or not.
However, a space for rotationally operating a hook wrench is necessary. Therefore, the tool is inadequate to be used in a situation where the space around a pipe connecting device is small, thereby causing a disadvantage of a limited service situation. In the disclosure of Patent Literature 3, the hook wrench is made of plastic so that it can be preferably used for rotating a synthetic-resin made union nut.
In a pipe connecting device, a work of fastening a union nut is completed when a screw advancement of the union nut due to fastening causes a tube pressing portion to strongly press a tube fitted onto a joint body and a sealed state is attained. In the configuration where a union nut is fastened with the hand and fingers, considerable effort must be exerted, but there is an advantage that a rapid torque increase caused by pressing of the tube pressing portion against the tube allows the fastening completion state or a state just before the completion to be detected in a relatively easy manner.
By contrast, in the configuration where fastening is performed by using a hook wrench by which the rotation force is amplified, the torque increase tends to be hardly sensuously detected as compared with the case where a union nut is directly operated by the hand and fingers. Therefore, there is a possibility that further disadvantages that a union nut is often excessively fastened, and that, conversely, fastening is ended in a state where a union nut is somewhat loosely fastened may occur.
Therefore, both the configuration where fastening is performed by the hand and fingers, and that where fastening is performed by using a hook wrench have advantages and disadvantages, and are adequately selectively used on a case-by-case basis.
As described above, a synthetic-resin made pipe connecting device is used in piping for a liquid which must be delicately handled in fields such as production of medical equipment and medicines, and food processing, and often disposed in complicated pipe equipment. Therefore, a pipe joint is often disposed in a very small space such as a place between a pump and tank which are placed near a wall or in a high place.
In both the configuration where fastening is performed by the hand and fingers, and that where fastening is performed by using a hook wrench, therefore, it is often that the space is so small that operation of a union nut is difficult, or that the fastening completion state is hardly checked. Particularly, leakage due to a failure in fastening or damage of a member caused by excessive fastening may occur. Even when either of the fastening structures is employed, therefore, the check of whether the fastening completion state is attained or not is very important.
As described above, in a pipe connecting device which is often disadvantageous in working conditions and space, the fastening completion state tends to be hardly recognized. Therefore, there is room for improvement with respect to “how to correctly recognize the fastening completion state”.    Patent Literature 1: Japanese Patent Application Laid-Open No. 2010-127421    Patent Literature 2: Japanese Patent Application Laid-Open No. 2010-127427    Patent Literature 3: Japanese Patent Application Laid-Open No. 2000-354973